Chalk Mt, Erath Co TX Alexanders 1870's

An early Erath County, Texas, settler, James David Alexander, I have been told by my uncles who were his grandchildren, left Virginia with several brothers and sisters at the outbreak of the Civil War. Born in 1848, he was about 13 when they left in 1861. The oldest brother's name has survived, Walter Alexander. He settled in Tarrant Co. Another brother might have been called Elias. Older brothers were killed in the Civil War.

There were sisters as well who came to Texas whose names I do not have, but am seeking.

James David first appears in my records when he marries Margaret Cordelia Snell in Brownwood, TX in 1872, aged 24. He and Margaret settle in Chalk Mountain, TX, Erath, Co. They have the following children: Frank Talmadge Alexander (b.1873), Ella May Alexander (b.1876), Nettie Maude Alexander (b.1879), Adron Alexander (b.1881,d.1882), and Cordelia Alexander (b.1884).

I am trying to ascertain James David's parents, siblings and place of birth.